The present invention relates generally to an earth observation system for observing the earth by operating a plurality of observation satellites. More particularly, the present invention is concerned with an earth observation system for operating the observation satellites ordinarily in a steady observation operation mode for observing globally the earth over the whole surface thereof while operating the satellites in a high-frequency observation operation mode for observing a given or particular district or local area on the earth with an increased observation frequency when occasion requires. Furthermore, the invention concerns a structure of the observation satellite, a sensor system for earth observation, an observation satellite operating ground system, and a data receiving system for the earth observation system. Moreover, the present invention also relates to an earth observation method and a program for allowing the observation method to be executed with the aid of a computer.
In the conventional earth observation system known heretofore, a single observation satellite is operated on and along a predetermined sun-synchronized quasi-recurrent orbit, wherein the number of days of a recurring period of the orbit, i.e., the number of days taken for the observation satellite to be able to observe again a same spot on the earth, is constant. The frequency of observation for a single given spot on the earth is in a range of once per several days to once per several weeks.
Thus, with the conventional earth observation system in which one observation satellite is operated on and along the predetermined orbit, it is certainly possible to observe globally and substantially uniformly the earth over the whole surface thereof. However, realization of the recursive observation of a given area or district on the earth will take a time interval as long as several days or several weeks. Thus, with the conventional observation satellite, it is impossible to effectuate a high-frequency observation of a given or particular district on the earth by maneuvering the satellite in a high-frequency observation operation mode which is of course favorable for observing a phenomenon, event or the like such as, for example, disaster occurring at a given or particular district on the earth.
Furthermore, even with the observation satellite equipped with an orbit control facility, correction of the orbit is possible only in conjunction with either the sun-synchronized quasi-recurrent orbit or the sun-synchronized recurrent orbit. To say in another way, any approaches or attempts for operating the satellite through combination of the sun-synchronized quasi-recurrent orbit and the sun-synchronized recurrent orbit have not yet been reported.